Various types of hearing prostheses provide persons with different types of hearing loss with the ability to perceive sound. Generally, hearing loss may be conductive, sensorineural, or some combination of both conductive and sensorineural. Conductive hearing loss typically results from a dysfunction in any of the mechanisms that ordinarily conduct sound waves through the outer ear, the eardrum, or the bones of the middle ear. Sensorineural hearing loss typically results from a dysfunction in the inner ear, including the cochlea where sound vibrations are converted into neural signals, or any other part of the ear, auditory nerve, or brain that may process the neural signals.
Example hearing prostheses include traditional hearing aids, vibration-based hearing devices, cochlear implants, and auditory brainstem implants. A traditional hearing aid, which is an acoustic stimulation device, typically includes a small microphone to detect sound, an amplifier to amplify certain portions of the detected sound, and a speaker to transmit the amplified sounds into the person's ear canal.
A vibration-based hearing device, which is also an acoustic stimulation device, typically includes a microphone to detect sound and a vibration mechanism to apply mechanical vibrations corresponding to the detected sound directly to a person, thereby causing vibrations in the person's inner ear. Vibration-based hearing devices include, for example, bone conduction devices, middle ear devices, and direct acoustic cochlear stimulation devices. A bone conduction device transmits vibrations corresponding to sound via the teeth and/or skull. A so-called middle ear device transmits vibrations corresponding to sound via the middle ear (i.e., the ossicular chain), without using the teeth or skull. A direct acoustic cochlear stimulation device transmits vibrations corresponding to sound via the inner ear (i.e., the cochlea), without using the teeth, skull or middle ear.
A cochlear implant provides a person with the ability to perceive sound by stimulating the person's auditory nerve via an array of electrodes implanted in the person's cochlea. A microphone coupled to the cochlear implant detects sound waves, which are converted into a series of electrical stimulation signals that are delivered to the implant recipient's cochlea via the array of electrodes. An auditory brainstem implant may use technology similar to a cochlear implant, but instead of applying electrical stimulation to a person's cochlea, the auditory brainstem implant applies electrical stimulation directly to a person's brain stem, bypassing the cochlea altogether. Electrically stimulating auditory nerves in a cochlea with a cochlear implant or electrically stimulating a brainstem may enable persons with hearing loss to perceive sound.
Further, some persons may benefit from a hearing prosthesis that combines two or more characteristics of a traditional hearing aid, vibration-based hearing device, cochlear implant, or auditory brainstem implant (e.g., two or more modes of stimulation) to enable the person to perceive sound. Such hearing prostheses can be referred to as bimodal hearing prostheses. Still other persons benefit from two hearing prostheses, one for each ear (e.g., a so-called binaural system generally or a bilateral system for persons with two cochlear implants).